Field of the Invention
The present invention relates to an optical system comprising a shared receiving channel for thermal and laser radiation which proceeds from a laser transmitter having an optical axis aligned parallel to the optical axis of the receiving channel, particularly for a thermal image device combined with a CO.sub.2 laser range finder, whereby a scan mirror, an IR optics and at least one detector arrangement are provided in the receiving channel in the direction of radiation incidence, and comprising a position sensor for synchronizing the transmission point in time of the laser pulses with the angular position of the scan mirror.
Description of the Prior Art
Thermal image devices whose detectors are generally disposed row-like forming a line, and operate in the wave length range of 8-14 .mu.m and which must be adequately cooled when operating are being increasingly employed for locating and targeting methods. To this end, all thermal image devices are equipped with a cooling system. Thermal image devices are combined with a laser range finder in order to be able not only to locate a subject emitting thermal radiation with a thermal image device but also to be able to measure the range of the located subject. This laser range finder can be integrated in the thermal image device. CO.sub.2 lasers having a receiving detector whose sensitivity lies in the 10 .mu.m range in accordance with the selected CO.sub.2 line and which must likewise be cooled have been more and more frequently proposed recently for laser range finders. It therefore lies at hand, given thermal image devices that are combined wtih such lasers, to use the expensive components of these devices, in particular the receiving optics, the detectors utilized for the thermal image device and for the laser range finder and, therefore, the cooling systems necessary for these signal receivers, as extensively as possible for both purposes. The themal image detectors already present are therefore co-employed for the reception of the laser radiation or both a detector row for the image generation of the thermal image device as well as a single detector or a plurality of detectors for the laser range finder are applied to a common carrier. Given such a detector arrangement, the further advantage also derives that the receiving optics of the thermal image device can also be co-employed for the receiver of the laser range finder. Only one shared cooling apparatus and one shared receiving optics are therefore required given a thermal image device combined with a laser range finder wherein the detectors of the thermal image device are disposed on a common carrier together with the detectors of the receiver for the laser range finder.
An apparatus in which the foregoing is realized is known, for example, from the German Pat. No. 30 48 809, fully incorporated herein by this reference. Given a thermal image device with a laser transmitter and a shared thermal image/laser receiving channel, a common sensor arrangement is thereby provided which is composed of a sequential arrangement of single detectors for thermal radiation and another arrangement of single detectors or at least a bar detector, the further arrangement extending perpendicular to the detector row from the center of the image field. Given this known apparatus as in standard thermal image devices, the image production occurs vertically by way of the detector row and laterally by way of beam deflection on the basis of an oscillating sensing or scan mirror. The line of sight directed to the target and, threfore, the laser beam aligned to the line of sight describe a line in the imaging plane (detector plane) at right angles to the detector row. A single or bar detector disposed on this line, for example one of the central detectors from the row or an additional single detector disposed laterally relative to the row, is therefore suited for the detection of the laser radiation reflected from the target subject for the purpose of range finding. Given such an apparatus, therefore, only one shared cooling apparatus and one shared receiving optics are required for the thermal image device and the laser range finder.
Given the apparatus known from the aforementioned German Pat. No. 30 48 809, the laser beam reflected by the target is conducted via the scan mirror which executes periodic movements about an axis for the purpose of scanning the scene on the basis of the detector battery of the thermal image device. As a consequence, the incorporation of one or more specially designed batteries for the laser radiation as well in addition to an interference filter in the Dewar vessel of the thermal image device and, at the same time, the synchronization of the transmission time of the laser pulses with the position of the scan mirror are required. In order to simplify the detector configuration provided for two different types of radiation given this known apparatus, a further apparatus, known from the German published application No. 31 04 318 and for the incorporation herein by this reference, provides that a linear detector battery is employed jointly for thermal and laser radiation, that the laser radiation is coupled out of the beam path immediately following the IR telescope before reaching the scan mirror and is subsequently focused via an optical assembly containing the IR lens onto detectors located in the edge regions of the detector battery. To this end, laser radiation and thermal radiation are separated in a spectral divider/deflector, whereby the laser radiation is imaged onto the selected laser detector of the battery via a following optical assembly comprising a laser receiving lens, an IR lens, a lens at the image field side and a further spectral divider which reflects the thermal radiation and allows the laser radiation to pass, and whereby the thermal radiation reflected by the scan mirror is coupled into the optical assembly and, threfore, is coupled back into the common receiving channel and is likewise focused in the detector plane by the further spectral divider. The adjustment of the laser beam onto the laser detector is thereby achieved by rotating the spectral divider/deflector about its longitudinal axis. Given the apparatus known from the German published application No. 31 04 318, therefore, one no longer depends on the center detector of the battery or on additional single detectors disposed laterally on a line at right angles to the battery and thereby proceeds on the basis that the ends of the detector battery for thermal radiation contain detectors which are not employed for the representation of the thermal image. Thermal image devices which have not been initially designed for receiving laser radiation can then be made useable for the reception of laser radiation in a corresponding manner in that detectors for the reception of laser radiation located at the edge regions of the battery are employed. However, a corresponding number of lines in the thermal image are thereby lost. As a consequence of the type of separation and combination of laser reception and thermal image channel provided given the apparatus of the German published application No. 31 04 318, however, an unmodified series sensor can be utilized for the simultaneous reception of thermal and laser radiation, so that existing thermal image devices can be made useful for receiving laser radiation without modification of the detector arrangement. For the purpose of achieving this advantage, the known apparatus, however, provides two optical assemblies that contain relatively large optical components. Such additional optical assemblies therefore require a relatively large amount of space. Given the integration of two optical assemblies in existing thermal image devices, this space requirement can lead to difficulties in view of accommodating space provided therein and can then require a more extensive modifications of existing devices. Furthermore, the two optical assemblies for separating and combining laser and thermal radiation are designed with spectral layers, so that optical losses must be accepted both for the laser radiation and for the thermal radiation. A further disadvantage is that, given utilization of a prescribed detector in the row or battery provided for the reception of thermal radiation also for the reception of laser radiation, the size of the detector in combination with the focal length of the thermal image device is not matched to the divergence of the laser transmission beam.
The problems revealed illustrate that, given the adaptation of an existing optical system serving for receiving thermal radiation and for simultaneously receiving laser radiation, i.e. given the combination of an existing thermal image device with a laser range finder, it is particularly difficult to modify the existing optical system or the existing thermal image device in a cost-effective manner with only a few components such that it can continue to be constructed with a series of standard, so-called common modules and such that only low optical losses are caused by the modification.